Rolling device for ring

ABSTRACT

A rolling apparatus is capable of rolling a metal ring to an accurate circumferential length and preventing the metal ring from dropping off. The rolling apparatus includes a metal ring support assembly having tension rollers  2   a   , 2   b  for supporting a metal ring W, a rolling roller  5  for rolling the metal ring W, a rolling assembly for pressing the rolling roller  5  against the metal ring W, a tension applying assembly having a tension cylinder  23  engaging tension roller support members  8, 10, 25 , on which one of the tension rollers  2   b  is rotatably supported, for displacing the tension roller  2   b  to apply tension to the metal ring W, and a rolling processing completing assembly  27  for detecting a completion of rolling of the metal ring W and inactivating the rolling assembly and the tension applying assembly. The rolling assembly has a first resilient member  18  interposed between the rolling cylinder  5  and its piston rod  15 . The tension applying assembly has a second resilient member  28  interposed between a piston rod  24  of the tension cylinder  23  and the tension roller support member  25.

[0001] This application is the national phase under 35 U.S.C. § 371 ofPCT International Application No. PCT/JP01/08706 which has anInternational filing date of Oct. 3, 2001, which designated the UnitedStates of America.

TECHNICAL FIELD

[0002] The present invention relates to an apparatus for rolling a metalring for use in a belt for a continuously variable transmission.

BACKGROUND ART

[0003] Laminated rings for use in belts for continuously variabletransmissions are manufactured by laminating a plurality of ring-shapedmembers having slightly different circumferential lengths. Thering-shaped members are prepared by welding opposite ends of a thinsheet of maraging steel, which is an ultrahigh strength steel, into acylindrical drum, and slicing the cylindrical drum into thin-sheet metalrings. The thin-sheet metal rings are then rolled into ring-shapedmembers having respective desired circumferential lengths.

[0004] One known apparatus for rolling such metal rings is disclosed inJapanese laid-open patent publication No. 11-290908. The disclosedapparatus has a pair of tension rollers spaced horizontally a givendistance from each other for supporting a thin-sheet metal ring thereon.The rolling apparatus also has a guide roller disposed intermediatebetween the tension rollers and a rolling roller for gripping androlling the metal ring in coaction with the guide roller.

[0005] The rolling roller is pressed against the metal ring by a rollingcylinder. At least one of the tension rollers is displaceable away fromthe other tension roller by a tension cylinder.

[0006] The rolling apparatus operates as follows: The metal ring istrained around the tension rollers. The rolling cylinder is actuated topress the rolling roller against the metal ring, which is grippedbetween the rolling roller and the guide roller. The rolling roller isrotated to roll the metal ring to progressively increase thecircumferential length of the metal ring. When the metal ring is rolled,the tension cylinder displaces at least one of the tension rollers awayfrom the other tension roller by a distance corresponding to theincrease in the circumferential length of the metal ring, thustensioning the metal ring. The displacement of the tension rollerprevents the metal ring from dropping off the tension rollers.

[0007] Then, the rolling apparatus measures the circumferential lengthof the metal ring which is progressively increased when the metal ringis rolled. When the circumferential length of the metal ring has reacheda desired value, the rolling process is finished. The circumferentiallength of the metal ring can be determined as a function of the distancebetween the axes of the tension rollers. The rolling apparatus uses anencoder, for example, for measuring the distance by which the tensionroller is displaced by the tension cylinder. The encoder detects acompletion of the rolling process when the distance by which the tensionroller is displaced reaches a given value. Then, the encoder outputs anelectric signal to stop the tension cylinder and the rolling cylinder.After the rolling cylinder is thus stopped, it releases the rollingroller from pressing the metal ring.

[0008] The rolling cylinder takes a time ranging from 0.01 to 0.1 secondin releasing the rolling roller from pressing the metal ring because ofa mechanical device used to release the rolling roller. During such atime, the rolling roller remains pressed against the metal ring, andcontinuously rotates due to the inertia from the rolling process. As aresult, the metal ring is excessively rolled after the rolling processis completed.

[0009] The tension cylinder and the rolling cylinder are separatemechanical arrangements which cause them to stop at different times,which are 0.01 to 0.1 second apart from each other, in response to theelectric signal from the encoder. If the stoppage of the rollingcylinder is delayed due to the stop timing difference, then the metalring may further be excessively rolled. Even if the rolling cylinder isstopped prior to the tension cylinder, the metal ring may further beexcessively rolled because of continued rotation due to the inertia.

[0010] When the metal ring is excessively rolled after the rollingprocess is completed, the tension ring has already been stopped.Therefore, no tension is imparted to the metal ring which is excessivelyrolled. As a consequence, the metal ring may possibly fall off thetension rollers.

DISCLOSURE OF THE INVENTION

[0011] It is therefore an object of the present invention to provide arolling apparatus which is capable of rolling a metal ring accurately toa predetermined circumferential length by eliminating drawbacks causedby different times at which a tension cylinder and a rolling cylinderare stopped.

[0012] Another object of the present invention is to provide a rollingapparatus which is capable of reliably preventing a metal ring fromdropping off after the metal ring has been rolled.

[0013] To achieve the above objects, there is provided in accordancewith the present invention an apparatus for rolling a metal ring,comprising metal ring supporting means having a pair of tension rollersfor supporting a thin-sheet metal ring thereon and a tension rollersupport member on which at least one of said tension rollers isrotatably supported, rolling means having a guide roller disposedintermediate between said tension rollers, a rolling roller for grippingand rolling the metal ring between the rolling roller and said guideroller, a rolling roller support member on which said rolling roller isrotatably supported, and a rolling cylinder having a piston rodconnected to said rolling roller support member for pressing saidrolling roller against said metal ring through said rolling rollersupport member, tension applying means having a tension cylinder havinga piston rod engaging said tension roller support member for applyingtension to said metal ring by displacing said least one of said tensionrollers through said tension roller support member to displace saidtension rollers relatively from each other when said metal ring isrolled by said rolling means, and rolling process completing means fordetecting a completion of rolling of said metal ring by measuring anamount of relative displacement of said tension rollers, andinactivating said rolling means and said tension applying means, saidrolling means having a first resilient member interposed between saidrolling cylinder and said piston rod thereof, for moving said piston rodin a direction to release said rolling roller from pressing said metalring when said rolling process completing means detects a completion ofrolling of said metal ring and inactivates said rolling means.

[0014] With the above arrangement, the first resilient member isinterposed between said rolling cylinder and said piston rod thereof.For rolling the metal ring, the rolling cylinder moves the piston rodagainst the bias of the first resilient member, thereby pressing therolling roller against the metal ring.

[0015] When the rolling process completing means detects a completion ofrolling of said metal ring and inactivates said rolling means, the firstresilient member returns immediately to its original state. The biasingforce of the first resilient member acts between the rolling cylinderand the piston rod. The piston rod is moved in a direction to releasethe rolling roller from pressing the metal ring. As a result, therolling cylinder releases the rolling roller from pressing the metalring without waiting for the mechanical arrangement thereof to move thepiston rod.

[0016] Therefore, after the rolling process completing means detects acompletion of rolling of said metal ring, the metal ring is preventedfrom being excessively rolled and has an accurate desiredcircumferential length.

[0017] The tension applying means comprises a second resilient memberinterposed between said tension roller support member and the piston rodof said tension cylinder, for causing said tension roller support memberto displace said least one of said tension rollers away from the othertension roller to apply tension to said metal ring when said rollingprocess completing means detects a completion of rolling of said metalring and inactivates said tension cylinder.

[0018] With the above arrangement, the second resilient memberinterposed between said tension roller support member and the piston rodof said tension cylinder. For rolling the metal ring, the tensioncylinder moves the piston rod to move the tension roller support memberagainst the bias of the second resilient member. As a result, thetension roller is displaced in a direction away from the other tensionroller. Consequently, the tension commensurate with the amount ofrolling of the metal ring is applied to the metal ring.

[0019] When the rolling process completing means detects a completion ofrolling of said metal ring and inactivates said tension cylinder, thesecond resilient member returns immediately to its original state. Thebiasing force of the second resilient member acts between the piston rodand the tension roller support member. The tension roller is urged in adirection away from the guide roller through the tension roller supportmember. As a result, even when the metal ring is excessively rolled bythe rolling means after the rolling process completing means detects acompletion of rolling of said metal ring, a displacement commensuratewith the elongation, or the increase in the circumferential length, ofthe metal ring due to the excessive rolling is imparted to the tensionroller support member. The metal ring is kept under tension and reliablyprevented from dropping off the tension rollers.

[0020] Both of the first and second resilient members may comprise aspring or a rubber member. The rubber member may be made or naturalrubber or synthetic rubber such as urethane resin or the like.

[0021] The rolling process completing means may comprise an armextending from said tension roller support member parallel to the pistonrod of said tension cylinder, a rotor rotatable in rolling contact withsaid arm, and a detector for detecting an amount of angular displacementof said rotor, and converting the amount of angular displacement of saidrotor into an amount of displacement of said arm to detect an amount ofdisplacement of said tension roller.

[0022] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwhen taken in conjunction with the accompanying drawings whichillustrate a preferred embodiment of the present invention by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a front elevational view, partly in cross section, of arolling apparatus according to the present invention;

[0024]FIG. 2 is an enlarged fragmentary plan view of a portion of therolling apparatus shown in FIG. 1;

[0025]FIG. 3 is an enlarged cross-sectional view illustrative of themanner in which the rolling apparatus shown in FIG. 1 operates; and

[0026]FIG. 4 is an enlarged cross-sectional view illustrative of themanner in which the rolling apparatus shown in FIG. 1 operates.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] As shown in FIG. 1, a rolling apparatus 1 according to thepresent invention has a pair of tension rollers 2 a, 2 b spacedhorizontally a given distance from each other for supporting athin-sheet metal ring W thereon. The rolling apparatus 1 also has abackup roller 3, a guide roller 4, and a rolling roller 5 which arevertically arrayed intermediate between the tension rollers 2 a, 2 b.The rolling apparatus 1 has a casing 7 mounted on a base 6 and having anopen front side for attachment and removal of the metal ring W. Thecasing 7 has recesses 7 a defined in its side walls laterally of therollers 2 a, 2 b, 4, 5.

[0028] The tension roller 2 a has a rear end rotatably supported on thecasing 7. The tension roller 2 a has a rear end rotatably supported on asupport member 8 which extends horizontally through one of the recesses7 a. The support member 8 is mounted on a slide member 10 that isslidably mounted on a rail 9 disposed on the base 6 laterally of thecasing 7. When the slide member 10 slides on the rail 9, the supportmember 8 displaces the tension roller 2 b away from the tension roller 2a. A mechanism for displacing the tension roller 2 b will be describedin detail later on.

[0029] The backup roller 3 is rotatably supported on a base unit 11mounted on the base 6 in the casing 7, and is disposed below anintermediate position between the tension rollers 2 a, 2 b. The guideroller 4 has a rear end rotatably supported on the casing 7, and ispositioned intermediate between the tension rollers 2 a, 2 b. The guideroller 4 grips the belt W trained around the tension rollers 2 a, 2 bbetween itself and the backup roller 3 and the rolling roller 5.

[0030] The rolling roller 5 is rotatably supported on a support member12 and disposed above the guide roller 3. The support member 12 isconnected by a flange 13 to a piston rod 15 of a rolling cylinder 14mounted on an upper wall of the casing 7. The piston rod 15 extendsvertically through the rolling cylinder 14, and has a piston 16 slidablealong an inner wall surface of the rolling cylinder 14. The piston rod15 has an end 15 a projecting upwardly from the upper end of thecylinder 14, and an engagement member 17 is threaded over the projectingend 15 a of the piston rod 15. A spring 18 as a first resilient memberis disposed between the upper end of the cylinder 14 and the engagementmember 17.

[0031] The interior of the rolling cylinder 14 is divided into an upperchamber 14 a and a lower chamber 14 b by the piston 16. When an oilpressure from an oil pressure unit (not shown) is supplied into theupper chamber 14 a, the piston 16 lowers the piston rod 15. When the oilpressure is supplied into the lower chamber 14 b, the piston 16 elevatesthe piston rod 15.

[0032] When the piston 16 lowers the piston rod 15, the rolling roller 5is pressed against the metal ring W and grips the metal ring W trainedaround the tension rollers 2 a, 2 b between the rolling roller 5 and theguide roller 4 supported by the backup roller 3. A motor (not shown) isdisposed behind the rear end of the rolling roller 5. The rolling roller5 is connected to the rotatable shaft of the motor through a universaljoint. When the motor is energized, therefore, the rolling roller 5 isrotated about its own axis. When rotated, the rolling roller 5 rolls themetal ring W that is gripped between the rolling roller 5 and the guideroller 4.

[0033] The mechanism for displacing the tension roller 2 b will bedescribed below.

[0034] A support column 19 is vertically mounted on the base 6 laterallyof the rail 9. The support column 19 supports thereon a first tensioncylinder 20 having a piston rod 21 extending therefrom which isconnected to a slide member 22 that is slidably mounted on the rail 9.Therefore, the slide member 22 is slidable back and forth along the rail9 by the piston rod 21.

[0035] A second tension cylinder 23 is mounted on the slide member 22and has a piston rod 24 extending therefrom which is connected to theslide member 10 on the rail 9 through a tubular member 25. The slidemember 10 is slidable back and forth along the rail 9 by the piston rod24 of the second tension cylinder 23.

[0036] The slide member 10 supports thereon the support member 8 onwhich the tension roller 2 b is rotatably supported, as described above.The support member 8 and the tension roller 2 b are movable back andforth in unison with the slide member 10.

[0037] The tubular member 25 attached to the slide member 10 is of ahollow cylindrical shape and houses therein a distal end of the pistonrod 24 which extends through a closed end of the second tension cylinder23. The tubular member 25 has a step 26 therein where the inner wall ofthe tubular member 25 closer to the second tension cylinder 23 issmaller in diameter than the inner wall of the tubular member 25 closerto the slide member 10. The step 26 is engageable with an engagementmember 27 of channel-shaped cross section on the distal end of thepiston rod 24. A spring 28 as a second resilient member is disposedaround the piston rod 24 axially between the closed end of the tubularmember 25 closer to the second tension cylinder 23 and the engagementmember 27.

[0038] As shown in FIG. 2, an encoder 30 is disposed on a mount 29placed on the base 6 behind the rail 9. A rotor 31 rotatably supportedon the encoder 30 is held in rolling engagement with an arm 32 whichextends parallel to the piston rod 24 and is attached to a rear end ofthe tubular member 25. The encoder 30 has a detector (not shown) fordetecting angular displacement of the rotor 31. The detector converts adetected amount of angular displacement of the rotor 31 into an amountof linear displacement of the arm 32, thus detecting an amount of lineardisplacement of the tension roller 2 b.

[0039] Operation of the rolling apparatus 1 shown in FIGS. 1 and 2 willbe described below.

[0040] The metal ring W is used as an element of a laminated ring foruse in a belt for a continuously variable transmission. The metal ring Wis prepared by welding opposite ends of a thin sheet of maraging steel,which is an ultrahigh strength steel, into a cylindrical drum, andslicing the cylindrical drum into an annular strip having a given width.The cylindrical drum is subjected to a solution treatment in order toremove welding strains.

[0041] In the rolling apparatus 1, the metal ring W is trained aroundthe tension rollers 2 a, 2 b from the open front side of the casing 7.Then, the first tension cylinder 20 is actuated to displace the slidemember 22 connected to the piston rod 21 along the rail 9 in a directionto displace the tension roller 2 b away from the tension roller 2 a. Thetension roller 2 a is not moved as it is rotatably supported on thecasing 7, and hence only the tension roller 2 b is displaced.

[0042] The second tension cylinder 23 is mounted on the slide member 22.Therefore, when the slide member 22 is displaced by the first tensioncylinder 20 as described above, the second tension cylinder 23 is alsodisplaced. As a result, the tension roller 2 b is displaced away fromthe tension roller 2 a through the piston rod f24 of the second tensioncylinder 23, the tubular member 25, the slide member 10, and the supportmember 8, thus applying a tension to the metal ring W trained around thetension rollers 2 a, 2 b. The first tension cylinder 20 is inactivatedwhen the second tension cylinder 23 reaches a position to start rollingthe metal ring W. The position to start rolling the metal ring W is aposition where the metal ring W trained around the tension rollers 2 a,2 b is kept taut under the applied tension.

[0043] Then, the rolling cylinder 14 is actuated to lower the piston rod15 against the bias of the spring 18. The piston rod 15 is guided by theflange 13 to press the support member 12 downwardly. The rolling roller5 rotatably supported on the support member 12 is lowered and pressedagainst the metal ring W. The non-illustrated motor is energized torotate the rolling roller 5 to start rolling the metal ring W which isgripped between the rolling roller 5 and the guide roller 4 supported bythe backup roller 3. At this time, the spring 18 is compressed betweenthe upper end of the rolling cylinder 14 and the engagement member 7.

[0044] When the metal ring W starts being rolled, its circumferentiallength is progressively increased. At this time, the first tensioncylinder 20 is inactivated, and the second tension cylinder 23 isactuated. As a result, at the same time that the rolling cylinder 14 isactuated, the tension roller 2 b is displaced away from the tensionroller 2 a. The displacement of the tension roller 2 b applies a tensioncommensurate with the increase in the circumferential length of themetal ring W to the metal ring W, thus keeping the metal ring W taut.

[0045] At this time, as shown in FIG. 3, the engagement member 27mounted on the distal end of the piston rod 24 engages the step 26 inthe tubular member 25 against the bias of the spring 28. The piston rod24 now displaces the tubular member 25 in a direction away from thetension roller 2 a. The slide member 10 on which the tubular member 25is mounted is displaced along the rail 9 in the same direction.

[0046] As a result, the tension roller 2 b rotatably supported on thesupport member 8 is displaced away from the tension roller 2 a by theslide member 10, thereby rolling the metal ring W while keeping themetal ring W taut. At this time, the spring 28 is compressed between theclosed end of the tubular member 25 closer to the second tensioncylinder 23 and the engagement member 27.

[0047] As the rolling process progresses, the amount of displacement ofthe tension roller 2 b is detected by the encoder 20 shown in FIG. 2.When the tension roller 2 b is displaced as described above, the arm 32extending from the tubular member 25 parallel to the piston rod 24 isalso displaced in the same direction as the tension roller 2 b. Theencoder 30 converts the amount of angular displacement of the rotor 31which rolls in contact with the arm 32 into an amount of lineardisplacement of the arm 32, and detects the amount of lineardisplacement of the arm 32 as an amount of linear displacement of thetension roller 2 b. When the encoder 30 detects that the amount oflinear displacement of the tension roller 2 b has reached apredetermined amount, the encoder 30 determines that the circumferentiallength of the metal ring W has reached a predetermined length. As aresult, the encoder 30 outputs an electric signal representing thecompletion of the rolling process, and the rolling cylinder 14 and thesecond tension cylinder 23 are stopped in response to the electricsignal.

[0048] In response to the electric signal, the rolling cylinder 14 stopssupplying the oil pressure into the upper chamber 14 a. At the sametime, the rolling cylinder 14 starts supplying the oil pressure into thelower chamber 14 b, causing the piston 16 to elevate the piston rod 15thereby to release the rolling roller 5 from pressing the metal ring W.

[0049] The rolling cylinder 14 takes a time ranging from 0.01 to 0.1second in releasing the rolling roller 15 from pressing the metal ring Wbecause of the above mechanical arrangement used to release the rollingroller 5. During this time, the rolling roller 15 remains pressedagainst the metal ring W, and continuously rotates due to the inertiafrom the rolling process. As a result, the metal ring W tends to beexcessively rolled after the rolling process is completed.

[0050] With the rolling apparatus 1 according to the present invention,however, when the rolling cylinder 14 is stopped after the rollingprocess is completed, the spring 18 tends to return immediately to itsoriginal free state from the compressed state. The biasing force of thespring 18 acts on the piston rod 15 through the engagement member 17, asindicated by the arrow in FIG. 1. As a consequence, the piston rod 15 ismoved upwardly as indicated by the imaginary lines in FIG. 1, releasingthe rolling roller 15 from pressing the metal ring W.

[0051] As described above, when the rolling cylinder 14 is stopped afterthe completion of the rolling process, the spring 18 acts to immediatelyrelease the rolling roller 15 from pressing the metal ring W. The actionof the spring 18 begins immediately, and does not wait for the operationof the mechanism arrangement of the rolling cylinder 14. Thus, the metalring W is reliably prevented from being excessively rolled, and isrolled accurately to a desired circumferential length.

[0052] Since the rolling cylinder 14 and the second tension cylinder 23are separate mechanical arrangements, they tend to stop at differenttimes, which are 0.01 to 0.1 second apart from each other, in responseto the electric signal from the encoder 30. If the stoppage of therolling cylinder 14 is delayed from the stoppage of the second tensioncylinder 23, then the metal ring W is further excessively rolled afterthe completion of the rolling process. Even if the rolling cylinder 14is stopped prior to the second tension cylinder 23, the metal ring Wtends to be excessively rolled after the completion of the rollingprocess because of continued rotation of the rolling roller 5 due toinertia from the rolling process. As a result, the metal ring W maypossibly be loosened around the tension rollers 2 a, 2 b.

[0053] With the rolling apparatus 1 according to the present invention,however, when the second tension cylinder 23 is stopped, the spring 28tends to return immediately to its original free state from thecompressed state. The biasing force of the spring 28 acts on the tubularmember 25, as indicated by the arrow in FIG. 4. As a consequence, if themetal ring W is further excessively rolled after the completion of therolling process, the tubular member 25 is displaced from the stoppedposition of the piston rod 24 in a direction away from the tensionroller 2 a. The displacement of the tubular member 25 tensions the metalring W to keep the metal ring W taut around the tension rollers 2 a, 2b.

[0054] Accordingly, even when the metal ring W is loosened by beingexcessively rolled as described above, the metal ring W is reliablyprevented from dropping off the tension rollers 2 a, 2 b.

[0055] In the illustrated embodiment, the spring 18 is disposed betweenthe upper end of the rolling cylinder 14 and the engagement member 17.The spring 18 may be disposed in the rolling cylinder 14, e.g., betweenthe lower end of the lower chamber 14 b and the piston 16. However, thespring 18 positioned outside of the rolling cylinder 14 as shown canmore easily be inspected and serviced for maintenance.

[0056] In the illustrated embodiment, the piston rod 25 of the secondtension cylinder 23 is connected to the slide member 10 through thetubular member 25, and the spring 28 is disposed between the piston rod24 and the tubular member 25. However, the spring 28 may be dispensedwith in order to roll the metal ring W accurately to a desiredcircumferential length. If the spring 28 is dispensed with, then thepiston rod 25 is directly connected to the slide member 10.

[0057] In the illustrated embodiment, the springs 18, 28 are used asresilient members. However, the springs 18, 28 may be replaced withelastomeric members made of natural rubber or synthetic rubber such asurethane resin or the like.

[0058] Industrial Applicability:

[0059] The rolling apparatus according to the present invention caneffectively be used as an apparatus for rolling a metal ring for use ina belt for a continuously variable transmission.

1. An apparatus for rolling a metal ring, comprising: metal ringsupporting means having a pair of tension rollers for supporting athin-sheet metal ring thereon and a tension roller support member onwhich at least one of said tension rollers is rotatably supported;rolling means having a guide roller disposed intermediate between saidtension rollers, a rolling roller for gripping and rolling the metalring between the rolling roller and said guide roller, a rolling rollersupport member on which said rolling roller is rotatably supported, anda rolling cylinder having a piston rod connected to said rolling rollersupport member for pressing said rolling roller against said metal ringthrough said rolling roller support member; tension applying meanshaving a tension cylinder having a piston rod engaging said tensionroller support member for applying a tension to said metal ring bydisplacing said least one of said tension rollers through said tensionroller support member to displace said tension rollers relatively fromeach other when said metal ring is rolled by said rolling means; androlling process completing means for detecting a completion of rollingof said metal ring by measuring an amount of relative displacement ofsaid tension rollers, and inactivating said rolling means and saidtension applying means; said rolling means having a first resilientmember interposed between said rolling cylinder and said piston rodthereof, for moving said piston rod in a direction to release saidrolling roller from pressing said metal ring when said rolling processcompleting means detects a completion of rolling of said metal ring andinactivates said rolling means.
 2. An apparatus according to claim 1,wherein said first resilient member comprises a spring or a rubbermember.
 3. An apparatus according to claim 1, wherein said tensionapplying means comprises a second resilient member interposed betweensaid tension roller support member and the piston rod of said tensioncylinder, for causing said tension roller support member to displacesaid least one of said tension rollers away from the other tensionroller to apply a tension to said metal ring when said rolling processcompleting means detects a completion of rolling of said metal ring andinactivates said tension cylinder.
 4. An apparatus according to claim 3,wherein said second resilient member comprises a spring or a rubbermember.
 5. An apparatus according to claim 1, wherein said rollingprocess completing means comprises an arm extending from said tensionroller support member parallel to the piston rod of said tensioncylinder, a rotor rotatable in rolling contact with said arm, and adetector for detecting an amount of angular displacement of said rotor,and converting the amount of angular displacement of said rotor into anamount of displacement of said arm to detect an amount of displacementof said tension roller.